122 



Hydration and Growth. 



The petioles of some young plants of a Solanum hybrid in the glass- 

 house at Tucson were available on April 21, 1918. Two series of sec- 

 tions were placed in distilled water and acid at 18 and 38 C., with 

 results shown in table 98. 



TABLE 98. 



TABLE 99. 



The swelling in distilled water was nearly three times as great at the 

 higher temperature, while in the acid solution a retardation took place 

 which limited the total at the higher temperature to something over 

 a half that possible at the lower point. The total swelling in acid at 

 the lower temperature occupied an hour and at the higher temperature 

 it was a matter of 10 or 15 minutes. A similar speeding-up of imbi- 

 bition in water was observed. The total capacity at the lower tem- 

 perature was not reached for 8 or 10 hours, while at the higher it was 

 something under 2 hours. 



Plants of Phaseolus which formed the experimental material for 

 measuring the growth of pods and seeds bore some pods in which the 

 beans were nearly mature. Pods of the same stage of development as 

 one which was under the auxograph for recording daily changes (see 

 p. 156) were opened and the unripe beans removed. The ends were cut 

 away and the outer coat removed. The remainder of each cotyledon 

 made one section, of which three were taken from separate pods for 

 swelling. The average thickness was 3.2 to 3.4 mm. and the swellings 

 of duplicate series were as given in table 99. 



The higher temperature to which series a was subjected appears to 

 be above the point at which maximum absorption or imbibition takes 

 place in distilled water, as the swelling was 30 per cent less than at the 

 lower temperature. The retarding effect is much more marked in the 

 acid solution, however, as the reduction of the total capacity below 

 that shown at 18 C. amounted to 40 per cent. 



The material in series b, taken at a later date and with seeds which 

 seemed to be more nearly mature, showed an increase in swelling in 

 distilled water of about 45 per cent over the total at the lower tempera- 

 ture, while the swelling in acid was less than half that at 18 C. The 

 average of the two series is such that the swelling in distilled water is 

 nearly the same at both temperatures, while in acid the average at 

 18 C. is 10.4 per cent, which is nearly double that at 38 C., at which 

 point the hydration capacity seems to be invariably lower than at the 

 lower temperature. These averages represent a total of 6 cotyledons 

 each. 



